docs: def get_cameras_signal_strength(self):
          """Return a list of signal strength of all cameras."""
          signal_strength = {}
          if not self.camera_properties:
              return None
  
          for camera in self.camera_properties:
              serialnum = camera.get('serialNumber')
              cam_strength = camera.get('signalStrength')
              signal_strength[serialnum] = cam_strength
          return signal_strength